<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script type="text/javascript">
    var num1=123; //1:456
    var num2=456; //2:456
    var num3=num1;     //:000
    num1=num2;
    num2=num3;

    alert(num1);
    alert(num2)

</script>
</body>
</html>